Optical-based recording systems such as compact-disk read only memory (CD ROM), video disk, write once read many (WORM), etc., are gaining wide acceptance in the marketplace because of their high storage capacity, random access capability, and relatively low cost. Moreover, erasable optical data storage systems (e.g., magneto-optical disk drives) are now commercially available, wherein old data stored on the optical media can be erased and new data written in place thereof.
The basic principle underlying typical optical recording systems involves the use of a light beam to write data to and read data from an optical medium. Typically, data is represented as a series of digital bits. A light source, such as a laser, is focused and directed by a lens assembly onto a circular optical disk. The disk is rotated about a spindle. By pulsing the laser, data is stored digitally onto the spinning optical disk. Subsequently, the stored data is read from the optical disk by detecting the light beam reflected from the optical disk.
A servo mechanism is used to locate the light beam in reference to fixed radial locations over the disk surface. Hence, the light beam is repositioned among numerous radial positions. As the servo mechanism sequentially moves the light beam radially across the spinning optical disk, a spiral, nearly-concentric circular groove, referred to as a "track," is described on the optical disk. It is onto the surfaces of these tracks that digital information is stored.
Accessing a different track involves utilizing the servo mechanism to position the lens assembly so that the beam is focused onto the target track. This process is known as a "seek." Often, data is written in a random manner. Consequently, a number of seeks are performed for a single disk access. Since data cannot be written onto nor retrieved from the disk when a seek is in progress, it is important to complete the seek as fast as possible in order to minimize undue delays.
In many prior an optical recording systems, the laser and the detector along with the lens assembly are moved as a package when performing a seek. Although this simple, straightforward seek method is precise, it is extremely slow. The laser, detector, and optics package constitutes a relatively large mass which renders it rather difficult to accelerate and decelerate quickly. In other words, this type of actuator has a relative long seek time due to its weight. Moreover, moving such a heavy package entails excessive power consumption. For portable, battery-operated systems, conserving power is critical.
One prior art method for reducing the payload of the actuator involves maintaining the laser and detector at fixed, stationary locations. Only the lenses and mirrors are moved in order to direct the light beam onto a desired track for a seek. Typically, the light generated by the laser is collimated and directed radially, parallel to the surface of the disk. A routing mirror is used to reflect the light beam downward towards the disk. An objective lens focuses the light beam onto the disk's surface. A seek is performed by moving the routing mirror in conjunction with the objective lens over radial locations of the disk.
Typically, either a linear or rotary type actuator is used to position the objective lens according to the servo mechanism. The routing mirror is held directly above the objective lens with an additional arm attached to the actuator. This additional arm adds to the mass of the payload which must be moved by the actuator. The additional weight causes the seek time to increase. Furthermore, it is important to maintain the mechanical and structural integrity of the arm so that it can withstand repeated start/stop shocks during seeks. Hence, the arm must be made relatively thick. The increased weight also contributes to excessive power consumption. Moreover, when the actuator comes to an abrupt stop at the destination track, the arm tends to vibrate. The setting time required for the vibration to subsist introduces an additional delay.
Therefore, what is needed is an apparatus and method for minimizing the payload to be moved by the actuator. It would be highly preferable if the requirement of having an additional arm to hold the routing mirror could be eliminated. Also, there is a need for directing the beam down towards the disk without requiring the use of a routing mirror in order to minimize the payload. Furthermore, there is a need in the prior art for minimizing parasitic mechanical resonances and system power dissipation.